DNA replication and DNA repair would be studied in Acholeplasma laidlawii. In vivo experiments center on DNA initiation studies using amino acid starvation and antibiotic inhibition of reinitiation. Restriction fragments containing the origin would be labeled and isolated. Origin-RNA species would be sought via hybridization to origin DNA fragments. Folded chromosomes would be isolated and their properties studied. Folded chromosomes and origin restriction fragments would be used to study the interaction of the chromosome with the cell surface (a membrane only) as a function of fatty acid content of the cell membrane. Temperature sensitive dna mutants would be sought in the C. Folsome A. laidlawii mutant collection. In vitro studies would use phage and plasmids as small replicon probes: coliphages M13, phiX174, and G4 DNA, and A. laidlawii phage MVL51, MVL2, and MVL3, would be used as substrates in vitro DNA synthesis studies comparing A. laidlawii and E. coli protein extracts. DNA replication proteins from A. laidlawii extracts would be isolated and studied. Transformation of A. laidlawii, A. laidlawii plasmids, and restriction-modification systems would be investigated. The primary cellular target for transformation of a cell into a malignant cell is the cellular DNA. Detailed knowledge of DNA replication and DNA repair processes are critically important in understanding this transformation process. Most Mycoplasmatales are parasitic, and some are pathogenic for important domestic animals and for man, demonstrating their economic and medical importance. Thus, this project would study critically important processes to the cancer problem, in organisms of direct medical and economic importance, demonstrating its direct relevance to the health sciences.